A. Field of the Invention:
The invention relates to the handling of sheet material and, more particularly, is directed to a method and apparatus for collecting a continuous flow of sheet while simultaneously discharging sheet piles of predetermined size.
B. The Prior Art:
Sheets, particularly of paper, may issue from a sheeting machine which shears the sheets from a continous web. The sheets are advanced seriatim along a delivery conveyor system to a collector device where the sheets collect into piles. Some form of mechanism is required to accommodate the growing stack in the collector. One known mechanism enables the delivery unit to be raised in concert with the growing stack; whereas the more typical assembly causes the sheets to collect on a reciprocable platform or table which descends at the growing rate of the stack. Whatever system is employed, there comes a time when the stack reaches a predetermined size for packaging, which may range in height from one inch or less to several feet, and the stack must be removed. Stack removal has represented a fundamental problem with sheet handling. All the heretofore schemes which successfully collect and discharge sheet stacks from a collector have involved compromises in versatility, efficiency, operator accessibility, and mechanical simplicity.
One approach has been to use two collection and discharge stations to which delivery flow of sheet is alternately diverted after a preset number of sheets is sensed by an electronic counter. The disadvantage with this approach has been that it requires complex machinery and essentially requires the cost of a second collector station.
Another common practice has been to interrupt or hesitate the flow of sheets along the delivery conveyor while a stack is being removed from the collector. The deceleration and acceleration periods often cause erratic machine performance, which may result in haphazard stacks.
A further approach has been to utilize a primary tray in the collector to accumulate a sheet stack and a second tray nearby to act as a waste collection bin. After the predetermined number of sheets have collected in the primary tray, sheet flow is diverted into the secondary tray. Rods are then moved into place over the top of the finished stack in the primary tray. The sheet flow is transferred back into the collector such that the sheets accumulate on top of the rods, while the primary tray is lowered away for removal of the completed stack. The emptied primary tray is returned to the collector, whereupon the rods are withdrawn, depositing the sheets which have accumulated thereon into the primary tray. Sheet flow continues into the primary tray and the process repeats. The problem with this approach is that the waste tray must be periodically emptied and readjusted for changes in sheet size and grade. Further, in order to avoid wasting sheets collected in the second tray, extra mechanical devices may be required to render stacks accumulating in the second tray fit for packaging.
U.S. Pat. No. 4,162,649 to John Thornton discloses a still further approach in which sheets delivered into a collector accumulate on a table moving downwardly in accordance with the growing rate of the stack. The stack is divided into desired batches of sheets by means of horizontal bars applied from behind the collector and placed between successive sheet deliveries. A divider is moved progressively downward with the table until it is ultimately arrested by a crosshead member. As the stack continues to descend, a gap is created between the underside of the divider and the uppermost sheet of the batch of sheets on the table. Creation of this gap generates a signal which causes a sheet support plate to travel forward into the stack and completely divorce the main stack from the batch resting on the table. The support plate travels downwardly at the growing rate of stack; while the table now moves downward at a higher speed to convey the separated batch of sheets to a discharge station where the batch is removed from the table. The emptied table is returned to the collector, whereupon the sheet support plate is withdrawn and deposits the stack back onto the table for the process to repeat. Some drawbacks with this system are that access into the collector from behind is precluded by the divider and that a cumbersome drive and travel guidance arrangement is necessary to permit the correlated movement of the support plate in the collector.
The present invention enables sheet delivery flow into a collector to be smooth and continuous, while simultaneously separating and removing sheet batches of predetermined size from the collected stack. The present invention uses a simplified mechanical arrangement which is relatively less wasteful of space without compromising production efficiency or stack quality. The invention has other advantages over prior art schemes as those skilled in the art will appreciate from the discussion below.